A power source device having a plurality of battery cells, includes a detection circuit for always monitoring a voltage in each of the secondary battery cells, a temperature, or the like in order to prevent abnormal states in the battery cells of over-charge, over-discharge, or the like. The detected voltages are also used for correctly estimating the remaining capacity (=State Of Charge: SOC) of an assembled battery. Especially, as a lithium ion battery can be used in the wide range of SOC, the over-charge range or the over-discharge range is close to the normal using range, and then it is necessary to more strictly manage the voltages in lithium ion batteries than other type of batteries.
The following is known. The plurality of the battery cells are assembled into the battery block, and this can downsize the power source device. This type of the power source device can also include a rigid circuit board including a detection circuit, and a wiring module which modularizes wirings connecting the detection circuit and the battery cells. A flexible printed circuit board suitable for modularizing may be used as the wirings (Patent Literature 1). The flexible printed circuit board can easily deform the wirings while binding the wirings, and can provide the wiring module of good assemblability.
The flexible printed circuit board is configured of conductive foils as conductive part, and a flexible insulating film. It is known that a cupper foil is used as the conductive foil, and the insulating film is made of polyimide or the like.
A power source device of Patent Literature 1 has a plurality of battery cells, a rigid circuit board including a detection circuit, and a flexible printed circuit board including wirings connecting the detection circuit and the battery cells. The flexible printed circuit board has connecting members at one end thereof, and is connected to electrode terminals of battery cells or bus-bars which connect the electrode terminals each other, through connecting members. The flexible printed circuit board is directly soldered to the rigid circuit board.